Sensor device and method for interrogating a sensor device

ABSTRACT

A sensor device includes i sensor elements of a first type and j additional sensor elements of a second type, the i sensor elements of the first type being connected in a circuitry (n×m) matrix array with n row conductors and m column conductors, where i, j, n and m are natural numbers other than zero and where 1≦i≦n*m. Each of the i sensor elements of the first type is connected between one of the n row conductors and one of the m column conductors and each of the j additional sensor elements of the second type is connected between two of the n row conductors.

FIELD OF THE INVENTION

The present invention relates to a sensor device comprising severalvariable-resistance sensors interconnected in a matrix array.

BACKGROUND OF THE INVENTION

In order to interrogate (i.e. read out) variable-resistance sensorelements, such as pressure-sensitive resistances or thermistors, anelectrical test voltage is applied to the sensor element and the currentresulting from the voltage applied is measured. This allows theinstantaneous electrical resistance of the sensor element to becalculated, from which the variable to be measured (pressure,temperature etc.) can be determined.

A sensor device with pressure-sensitive sensors may, for example, beused in a seat occupancy detection function to control an activepassenger restraint system in a vehicle. A sensor mat of this kindcomprises several individual pressure-sensitive sensors integrated intothe seat and distributed over the surface of the passenger seat. Thesesensors are connected to an analysing unit, which checks the triggeredcondition of the individual sensors. If the seat is occupied by aperson, several of the sensors are triggered by the force exerted by theweight of a person on the seat, and this condition is recognised by theconnected analysing circuit as indicating that the seat is occupied.This information is then passed on to the airbag control system.

In order to allow the sensors to be interrogated selectively, each ofthe sensors must in principle be connected to the analysing circuit. Inorder to reduce the number of connecting conductors, it is advisable tooperate the individual sensors in a matrix array. This means that, for aquantity of n*m sensor elements, n row conductors and m columnconductors are basically provided, each of the sensor elements beingconnected between one row conductor and one column conductor.

It should be noted that a matrix array of this kind constitutes acircuitry configuration. In other words, a matrix array in a realconfiguration does not require that the sensor elements be arranged in aregular grid layout, nor does it require that the individual connectingconductors run in straight lines parallel or perpendicular to oneanother.

The procedure for analysing a configuration in which sensors areinterconnected in a matrix array is as follows. First the whole matrixarray, with the exception of a first column conductor, is set to thesame potential, e.g. to ground. A test voltage is then applied to thefirst column conductor, after which the current flowing through theindividual row conductors is measured selectively. This allowsresistance values to be determined selectively for those sensor elementswhich are connected between the first column conductor and the variousrow conductors. If this procedure is repeated for each of the columnconductors, all the sensor elements can be measured selectively, oneafter the other. It should be noted here that, as an alternative meansof interrogating the individual sensor elements, it is possible to applythe test voltage to each row conductor and measure the current passingthrough the sensor elements at the column conductor.

If the number of sensors in a sensor mat of this kind is to beincreased, generally speaking the number of connecting conductors mustalso be increased. This means, for example, that if the (n×m) matrix isextended to an ((n+1)×m) matrix, another row conductor will have to beintroduced to incorporate the additional sensors into the matrix array.

In practice, however, such an increase in the number of connectingconductors leads to several problems. For instance, having a largenumber of conductor paths leads to difficulties in designing the shapeof the sensor mat. The individual sensors in a seat occupancy sensor,for example, are arranged in a sandwich structure consisting of twocarrier films and a spacer which, on the one hand must form a coherentwhole, but on the other hand must cover as small an area as possible ifseat comfort is not to be impaired. The individual sensors are thereforeconnected to one another simply by narrow bridges in the sandwichstructure through which the connecting conductors of the sensors mustrun. Increasing the number of required connecting conductors makes itmore difficult to run the conductors through the narrow connectingbridges, or makes it necessary to widen the connecting bridges, whichmakes a sensor mat of this kind in a vehicle seat more noticeable.

On the other hand, the number of connecting conductors can only beincreased if the analysis circuit has a corresponding number of inputsand outputs respectively. Indeed, each row conductor and columnconductor must be connected to the analysis circuit so that either atest voltage can be applied to the conductor concerned or the currentflowing through the conductor can be measured. Increasing the number ofconnecting conductors therefore results in a more complicated and hencemore expensive analysis circuit.

SUMMARY OF THE INVENTION

The purpose of the present invention is therefore to propose a sensordevice which has a higher number of sensors while the number ofconnecting conductors remains the same.

This purpose is achieved by means of a sensor device according to thepresent invention. Such a sensor device comprises i sensor elements of afirst type which are interconnected in a circuitry (n×m) matrix arraywith n row conductors and m column conductors, where i, n and m arenatural numbers other than zero, and where 1≦i≦n*m. It should be notedthat a matrix array of this kind constitutes a circuitry arrangement.This means that a matrix array in a real arrangement does not requirethat the sensor elements be arranged in a regular grid layout, nor doesit require that the individual connecting conductors run in straightlines parallel or perpendicular to one another. Each of the i sensorelements is connected between one row conductor and one columnconductor.

According to the present invention, the sensor device has j additionalsensor elements of a second type, where j is a natural number other thanzero, each of the j additional sensor elements of the second type beingconnected between two row conductors. Alternatively, the sensor devicemay have k additional sensor elements of a second type, where k is anatural number other than zero, each of the k additional sensor elementsof the second type being connected between two column conductors.

In addition to the standard, conventional matrix array of sensorelements, the device proposed in the present invention includes one ormore additional sensors, each of which is connected between either tworow conductors or two column conductors. In both cases it is possible tointerrogate the additional sensor elements individually without the needto incorporate additional connecting conductors into the sensor devicefor this purpose. In this case the term “connecting conductors” simplyrefers to row or column conductors which must be led out of the sensordevice and connected directly to the analysis circuit. It follows thatthis term should not be applied to the conductor paths by which theadditional sensor elements are connected to the respective row or columnconductors.

In order to individually analyse the sensor elements in the traditionalmatrix array, the same procedure is used as for a conventional matrixarray. To this end the whole matrix array with the exception of a firstcolumn conductor is first set to the same potential, e.g. to ground. Atest voltage is then applied to the first column conductor, after whichthe current flowing through the individual row conductors is selectivelymeasured. This allows the resistance values of the sensor elementsconnected between the first column conductor and the various rowconductors to be determined selectively. By repeating this procedure foreach of the column conductors it is possible to measure all of thesensor elements selectively, one after the other. It should be notedhere that, as an alternative, the test voltage can be applied to theindividual row conductors, and the individual sensor elements can thenbe interrogated by measuring the current flowing through them at thecolumn conductors. In this procedure the additional sensor elements donot interfere with the interrogation of the conventional sensor elementsbecause, as a consequence of the measurement method, they are at thesame voltage at both contact points, and are therefore not included inthe measurement result.

A similar method is used in order to read out each of the additionalsensor elements which have been connected between two column conductors.First the whole matrix array, with the exception of a first columnconductor, is set to the same potential, e.g. to ground. A test voltageis then applied to the first column conductor, after which the currentflowing through the other column conductors is measured selectively.This allows resistance values to be determined selectively for thosesensor elements which are connected between the first column conductorand one of the other column conductors. If this procedure is repeatedfor each of the column conductors, all the sensor elements connected inthis way can be measured selectively, one after the other. A similarmethod is used to read out each of the sensor elements which have beenconnected between two row conductors. Once again it should be noted thatthe sensor elements arranged in the conventional matrix array do notaffect the results of measurements on the additional sensor elements,because as a consequence of the measurement procedure used they are atthe same voltage at both contact points, and are therefore not includedin the measurement result.

The advantage of the configuration proposed in the present invention istherefore that it allows additional sensor elements to be measuredwithout the need for additional wiring, and without interfering with theconventional method of measuring matrix components at the points ofintersection between row and column conductors. Existing analysiscircuits can therefore be used without modification with this extendedsensor configuration, in which case the extension is not used, but doesnot interfere with normal operation.

In all of the above measurement steps the columns and rows are selectedeither directly using drivers and amplifier circuits on each row andcolumn or by using individual drivers and measurement amplifiersconnected via a multiplexer to the rows or columns which are to bemeasured or selected. In a particular advantageous embodiment, a deviceto interrogate the sensor elements comprises n+m control devices, whichcan be connected to the n row conductors and the m column conductors,each control device being designed to be individually switchable in sucha way that in a first mode it can operate as a driver cell to apply atest voltage to the row or column conductor to be connected, and in asecond mode it can operate as a measuring transformer to process thesignal at the column or row conductor which is to be connected. Ananalysis circuit of this kind allows the individual rows or columnconductors to be selected in a particularly flexible manner, which inturn allows measurements to be made between both a single row conductorand a single column conductor, and also between two row conductors ortwo column conductors.

In a particular advantageous embodiment of the sensor device, the devicecomprises j+k additional sensor elements of a second type, where j and kare both natural numbers other than zero, with each of the additionalsensor elements of the second type connected between two columnconductors or two row conductors. By extending the conventional sensormatrix in both dimensions, i.e. as well between row conductors asbetween column conductors, it is possible to optimise the number ofsensor elements which can be interrogated using the same number ofconnecting conductors. This approach allows a maximum of

$\frac{n*\left( {n - 1} \right)}{2}$additional sensor elements to be connected between the n row conductorsand

$\frac{m*\left( {m - 1} \right)}{2}$additional sensor elements to be connected between the m columnconductors. It will be clear to the skilled person that, depending onthe application and the requirements, it is also possible to incorporatefewer additional sensor elements into the conventional matrix array. Itshould be noted that the sensor elements of both the first and secondtypes can be designed in such a way that they perform an identicalfunction in the sensor device. To this end the different types of sensorelement may, for example, be configured identically. Alternatively, thesame function, such as pressure measurement, of the two types of sensorelement can also be performed with a different structural form. In thecase of a sensor mat using so-called film pressure sensors, the sensorelements of the first type may, for example, be designed in such a waythat they operate in through mode, while the sensor elements of thesecond type may operate in shunt mode.

In the case of film pressure sensors which operate in trough mode, afirst contact is arranged on a first carrier film and a second contactis arranged on a second carrier film, both carrier films beingpositioned a certain distance apart in such a way that the two contactsare facing one another. A layer made of a semiconducting material isarranged between the two contacts, which is pressed against the twocontacts when the sensor is triggered. The resistance between the twocontacts varies according to the pressure applied. This type of sensoris particularly suitable for producing sensor mats because in thisdesign the row conductors are printed onto one carrier film while thecolumn conductors can be arranged on the other carrier film. Thisarrangement of the various connection paths on different carrier filmsdoes not cause any problems at the points of intersection between thevarious connecting conductors because the latter run at differentlevels.

Film pressure sensors operating in shunt mode have two contacts arrangedon a first carrier film at a certain distance from another. On a secondcarrier film spaced from the first a semiconducting layer is mounted insuch a way that it covers the area between the two contacts, bringingthe two contacts into contact when the carrier films are pressedtogether. This type of sensor is therefore particularly suitable as adesign for the additional sensor elements, because both contacts aredeposited on a single carrier film, and are therefore easy to contactwith the row or column conductors on this carrier film.

In an advantageous embodiment of the sensor device, at least one of thesensor elements of the second type is designed in such a way that the atleast one sensor element of the second type performs a function in thesensor device, which is different from the function performed by thesensor elements of the first type. Such a sensor element with adifferent function might, for example, allow environmental influences tobe monitored and/or compensated for. In this way several compensationelements can be introduced into a conventional sensor device in a matrixarray which will, for example, allow temperature influences to becompensated for without degrading the resolution of the original sensormatrix.

It should be noted that a few of the additional sensor elements mayperform the same function as the i normal sensor elements, while otheradditional sensor elements may perform a different function in thesensor device.

BRIEF DESCRIPTION OF THE DRAWINGS

The text which follows describes various embodiments of the inventionwith reference to the attached illustrations. These show:

FIG. 1: a sensor device in a matrix array with additional sensorelements which are connected between the row conductors.

FIG. 2: a sensor device in a matrix array with additional sensorelements which are connected between the column conductors.

FIG. 3: a useful circuit for interrogating a sensor device withadditional sensor elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an first embodiment of an improved sensor arrangement.Sensor arrangement 10 comprises several row conductors 112, 114, 116 and118 as well as several column conductors 120, 122, 124, 126 and 128. Thedesign shown is therefore a (4×5) matrix array. At each intersectionpoint between one of row conductors 112, 114, 116 and 118 and one ofcolumn conductors 120, 122, 124, 126 and 128 a sensor element 130(depicted as a resistance) is connected in a conventional manner betweenthe respective row and column conductor. In the (4×5) matrix arrayshown, 4*5=20 sensor elements 130 can be connected in this way. Thesesensor elements 130 might, for example, include pressure-sensitiveresistances or thermistors.

In addition to the sensor elements 130, other sensor elements 132 arepresent in the present sensor arrangement 10, each of which is connectedbetween two of row conductors 112, 114, 116 and 118. Between each pairof rows 112–114, 112–116, 112–118, 114–116, 114–118 and 116–118 anadditional, individually interrogateable sensor element 132 can beconnected. In the configuration shown with four row conductors it istherefore possible to incorporate a maximum of six additional,individually interrogateable sensor elements 132. It will be easy forthe skilled person to verify that the maximum number (j_(max)) ofadditional sensor elements 132 obeys the formula

${j_{\max} = \frac{n*\left( {n - 1} \right)}{2}},$where n represents the number of row conductors available.

The sensor arrangement shown in FIG. 2 should be regarded as essentiallysimilar to that shown in FIG. 1. Unlike the embodiment described above,in this embodiment additional sensor elements 134 are connected betweencolumn conductors 120, 122, 124, 126 and 128. Between each pair ofcolumns 120–122, 120–124, 120–126, 120–128, 122–124, 122–126, 122–128,124–126, 124–128 and 126–128 an additional, individually interrogateablesensor element 134 can be connected. In the configuration shown withfive column conductors it is therefore possible to incorporate a maximumof ten additional, individually interrogateable sensor elements 134. Itwill be easy for the skilled person to verify that the maximum number(k_(max)) of additional sensor elements (134) obeys the formula

${k_{\max} = \frac{m*\left( {m - 1} \right)}{2}},$where n represents the number of column conductors available.

It should be noted that in order to make full use of the interconnectionpossibilities offered by the available row and column conductors,additional sensor elements can be incorporated into the matrix array inboth dimensions. A design of this kind is essentially a combination ofthe two designs in FIG. 1 and FIG. 2. The maximum number of individuallyinterrogateable sensor elements 132 and 134 that can be incorporatedinto the conventional matrix array in this way is therefore

${j_{\max} + k_{\max}} = {\frac{n*\left( {n - 1} \right)}{2} + {\frac{m*\left( {m - 1} \right)}{2}.}}$

FIG. 3 shows an advantageous arrangement for interrogating the sensordevices described above. The actual sensor arrangement 10 (in this casea (4×4) matrix) is not shown in full here. In the interests of clarity,the illustration shows only two of the sensor elements 130 and one eachof the additional sensor elements 132 and 134, but it will be clear tothe skilled person that corresponding sensor elements 130, 132 and 134could also be connected between the other column and row conductors orbetween the respective row conductors and/or between the respectivecolumn conductors.

Sensor arrangement 10 is connected via a plug or clamp connector 30 tothe device 32 for interrogating the sensor elements. This deviceincludes several control devices 36, preferably arranged in a commonhousing 34, each of which can be connected to one of row or columnconductors 12–18 and 20–26 via the plug or clamp connector. Once again,in the interests of clarity the illustration shows only a few of thecontrol devices 36.

Each control device 36 comprises a negative feedback operationalamplifier 38 whose negated input 40 can be connected to the respectiverow or column conductors 12–18 and 20–26, and whose non-negated input 42can be switched between a connection 44 to a drive voltage and aconnection 46 to a reference potential. This switching should preferablytake place via an electronically controlled switch 48. The referencepotential is represented by a virtual ground whose potential liesbetween the actual ground and the circuit's supply voltage, e.g. at halfthe supply voltage.

This embodiment makes use of the principle that a negative feedbackoperational amplifier 38 of this kind attempts to reduce the differencein voltage between the negated and non-negated inputs to zero. Thus if aspecific control device 36 is to work as the driver cell, e.g. thecontrol device connected to column conductor 20, the non-negated input40 of the operational amplifier 38 is connected to connection 44 of thedriver voltage. The operational amplifier 38 then drives column 20,which is connected to the negated input (40), via the negative feedbackresistance 50.

In order to interrogate the sensor elements 130 connected between columnconductor 120 and the various row conductors 112–118, the remainingcolumn conductors 122–126 and row conductors 112–118 must be set to thereference potential. To this end the non-negated inputs 42 of thecorresponding operational amplifiers 38 are connected to connection 46for the reference voltage. These operational amplifiers 38 then act ascurrent-voltage transformers which transform the current flowing throughwhichever row or column is connected, i.e. the current flowing via thesensor element 130 which is to be measured, into an output voltage atthe output 52 of the operational amplifier which is proportional to theresistance of the sensor element.

The resistance value of the negative feedback of the individualoperational amplifiers 38 should preferably be adjustable. In theembodiment shown, this is achieved by using a second negative feedbackresistance 54 which can be connected in parallel to the first negativefeedback resistance 50 by means of an electronically controlled switch56. This has the advantage of making it possible to adjust the measuringsensitivity of the control devices 36 which have been connected asmeasuring transformers, thus allowing a high level of accuracy to beachieved in measurements. Furthermore, using the variable negativefeedback resistances on the control devices which have been connected asdriver cells allows the current flowing into the sensor arrangement 10to be adjusted.

One possible measurement sequence using the device presented tointerrogate several sensor elements is as follows:

All the row and column conductors are first set to the referencepotential (i.e. the virtual ground) by connecting the non-negated inputs42 of the operational amplifiers 38 to the appropriate connection 46.Sensor configuration 10 is now unpowered and in idle state.

At the start of the measurement cycle, the non-negated input 42 of theoperational amplifier 38 of one column 120 is connected to theconnection 44 of the driver voltage. All the resistance values of thesensor elements 130 connected between the column conductor 120 and thevarious row conductors 112–118 can now be measured one after the other.

The non-negated input 42 of the operational amplifier 38 connected tothe column conductor 120 is then switched to the reference potentialagain and the next column, 122, is selected. In this way it is possibleto work through each of the columns in turn, after which the sensorelements 132 connected between the row conductors and the sensorelements 134 connected between the column conductors can be read out inthe same way. At the end of such a measurement cycle the resistancevalues of all the sensor elements 130, 132 and 134 will then have beendetermined. In a second measurement cycle it is then possible, once thenegative feedback resistances on the operational amplifiers 38 have beenchanged, to interrogate all the sensor elements in another measuringrange, for example. Comparing the two resistance values obtained allowsconclusions to be drawn about any defects in the matrix.

1. A sensor device comprising i sensor elements of a first type and jadditional sensor elements of a second type, the i sensor elements ofthe first type being connected in a circuitry (n×m) matrix array with nrow conductors and m column conductors, where i, j, n and m are naturalnumbers other than zero and where 1≦i≦n*m, wherein each of the i sensorelements of the first type is connected between one of said n rowconductors and one of said m column conductors and wherein each of the jadditional sensor elements of the second type is connected between twoof the n row conductors.
 2. The sensor device according to claim 1,comprising k additional sensor elements of a second type, where k is anatural number other than zero, wherein each of the k additional sensorelements of the second type is connected between two of the in columnconductors.
 3. The sensor device according to claim 1, wherein$1 \leq j \leq {\frac{n*\left( {n - 1} \right)}{2}.}$
 4. The sensordevice according claim 1, wherein the sensor elements of the first typeand the sensor elements of the second type are designed in such a waythat they perform an identical function in the sensor device.
 5. Thesensor device according to claim 1, wherein at least one of the sensorelements of the second type is designed in such a way that the at leastone sensor element of the second type performs a function in the sensordevice which differs from the function performed by the sensor elementsof the first type.
 6. The sensor device according to claim 1, furthercomprising a device for interrogating a sensor device including n+mcontrol devices which are connectable to the n row conductors and the mcolumn conductors, each control device being individually switchable insuch a way that in a first mode the control device operates as a drivercell for applying an electrical test voltage to the row or columnconductor to be connected, and in a second mode the control deviceoperates as a measuring transformer for processing the signal at thecolumn or row conductor which is to be connected.
 7. The sensor deviceaccording to claim 2, wherein$1 \leq j \leq {\frac{n*\left( {n - 1} \right)}{2}.}$
 8. The sensordevice according to claim 2, wherein$1 \leq k \leq {\frac{m*\left( {m - 1} \right)}{2}.}$
 9. The sensordevice according claim 2, wherein the sensor elements of the first typeand the sensor elements of the second type are designed in such a waythat they perform an identical function in the sensor device.
 10. Thesensor device according to claim 2, wherein at least one of the sensorelements of the second type is designed in such a way that the at leastone sensor element of the second type performs a function in the sensordevice which differs from the function performed by the sensor elementsof the first type.
 11. A sensor device comprising i sensor elements of afirst type and k additional sensor elements of a second type, the isensor elements of the first type being connected in a circuitry (n×m)matrix array with n row conductors and m column conductors, where i, k,n and m are natural numbers other than zero and where 1≦i≦n*m, whereineach of the i sensor elements of the first type is connected between oneof said n row conductors and one of said m column conductors and whereineach of the k additional sensor elements of the second type is connectedbetween two of the in column conductors.
 12. The sensor device accordingto claim 11, further comprising a device for interrogating a sensordevice including n+m control devices which are connectable to the n rowconductors and the m column conductors, each control device beingindividually switchable in such a way that in a first mode the controldevice operates as a driver cell for applying an electrical test voltageto the row or column conductor to be connected, and in a second mode thecontrol device operates as a measuring transformer for processing thesignal at the column or row conductor which is to be connected.
 13. Thesensor device according to claim 11, wherein$1 \leq {\left\lbrack \lbrack j\rbrack \right\rbrack\underset{\_}{k}} \leq {\frac{m*\left( {m - 1} \right)}{2}.}$14. The sensor device according claim 11, wherein the sensor elements ofthe first type and the sensor elements of the second type are designedin such a way that they perform an identical function in the sensordevice.
 15. The sensor device according to claim 11, wherein at leastone of the sensor elements of the second type is designed in such a waythat the at least one sensor element of the second type performs afunction in the sensor device which differs from the function performedby the sensor elements of the first type.